A standard coke-oven door has a membrane whose center portion is fixed via mounting blocks to the door structure and whose periphery is equipped with a blade-type seal that is pressed by spring units against the annular door jamb of the coke oven. The membrane can deform to follow thermal deformations of the various parts which in use are heated greatly. The mounting blocks are attached to a backing plate of a large door plug normally formed at least partially of refractory material so that the door plug serves primarily to hold the material in the coking chamber while the membrane serves mainly to prevent gases and heat from escaping. During use the door is subjected to enormous thermal stresses and deforms as a result so that the spring units keep the blade-type seal pressed against the door jamb with some deformation of the membrane.
As described in German patent document 2,755,029 of T. Ikio et al the mounting blocks are carried via stacks of spring washers on the door frame so that they can move somewhat and at least partially follow the movement of the membrane. This is intended to reduce deformation of the membrane as such deformation eventually leads to its failure. Even so, the service life of the membrane is very short compared to the other elements of the coke oven, so that the entire battery must be brought down periodically for replacement of damaged and leaking membranes.